The present invention provides an enclosure for protecting electrical components installed in a location where a flammable gas or vapor is expected to be present.
Enclosures may be used to provide protection for an electrical component such as, for example, an electrical switch, a motor starter, a motor, or an electrochemical fuel cell. These enclosures are typically accessible by opening so that the electrical component placed within the enclosure housing may be accessed and/or serviced. Thus enclosure housings typically comprise at least two pieces that fit together to provide a protective enclosure around the electrical component. In addition to protecting the electrical component against physical damage, in locations where a flammable gas or vapor may be present, it is also desirable for the enclosure to protect the electrical component from exposure to combustible concentrations of the flammable gas or vapor which the electrical components may ignite. So called xe2x80x9crestricted breathingxe2x80x9d enclosures typically employ gaskets or other sealing mechanisms between separate housing pieces to improve the sealing between the separate pieces. Restricted breathing enclosures are constructed so that the likelihood of a surrounding atmosphere entering the enclosure is reduced to as low a level as possible.
However, gasketed or xe2x80x9csealedxe2x80x9d enclosures can not guarantee complete sealing against the penetration of flammable gases by diffusion. This is especially true for gases with a high diffusion rate, such as hydrogen. In addition, it is also believed that even gasketed enclosures xe2x80x9cbreathxe2x80x9d (i.e. fluids pass between the surrounding atmosphere and the enclosure interior). Breathing may be induced by pressure differentials between the enclosure interior and the surrounding atmosphere. Such pressure differentials are affected by temperature changes caused when heat producing components are operated within the enclosure. There may also be other causes for flammable fluid penetration into the interior of an electrical component enclosure, such as, for example, defects in the seal or misalignment of the seals. Furthermore, in addition to flammable fluids which may originate from the atmosphere surrounding the enclosure, flammable fluids may also originate inside the enclosure from electrical components themselves, such as, for example, electrochemical fuel cells.
Therefore, unsealed or even xe2x80x9csealedxe2x80x9d openable equipment enclosures, may allow flammable fluids to accumulate therein because of diffusion, breathing, or internal generation of flammable fluids. Thus, when an enclosure is installed in a location where a flammable fluid is expected to be present, it is recognized that there is a potential for a combustible concentration of the flammable fluid to accumulate within the enclosure. Accordingly, for electrical components capable of igniting flammable fluids, electrical codes require particular types of enclosures to be used when such components are installed in a location where a flammable fluid is expected to be present. The nature of the required enclosure depends upon the likelihood and expected frequency of a flammable fluid being present, and other factors such as the likely duration of exposure and the concentration of the flammable fluid. Because these factors may be different at different locations, some electrical codes define different zones which reflect the degree of exposure associated with locations where a flammable fluid is expected to be present.
For example, the Canadian Electrical Code defines such locations as being a Zone 0, Zone 1, or Zone 2 location. A Zone 0 location refers to locations where there is the greatest exposure to a flammable fluid. In a Zone 0 location, a flammable fluid atmosphere is expected to be present either continuously or for long periods. A Zone 1 location refers to the next level of exposure to a flammable fluid. For example, Zone 1 typically refers to locations where exposure to a flammable fluid is not continuous, but a flammable fluid atmosphere is likely to occur either during normal operation, or frequently because of repair or maintenance operations, or because of leakage. Also, a location may be classified as a Zone 1 location if it is adjacent to a Zone 0 location from which flammable fluid atmospheres could be communicated. A Zone 2 location typically refers to a location where there is a possibility of exposure to a flammable fluid, but the likelihood of such an exposure is less than in a Zone 0 or Zone 1 location. For example, exposure to a flammable fluid may occur during system upsets or by being adjacent to a Zone 1 location where a flammable fluid is expected to be present. In Zone 2 locations, exposure to flammable fluid is not likely to occur during normal operation, and if flammable fluid is present, for example, because of a system upset, the flammable fluid is only expected to be present for a short period of time. The aforementioned Canadian Electrical Code generally conforms with international electrical codes such as, for example, International Standard IEC 79-15: 1987. 
The Canadian Electrical Code sets out the type of electrical component enclosure that must be used in Zone 0, Zone 1 and Zone 2 locations. For example, the Canadian Electrical Code requires a special flame-proof enclosure for most electrical components installed in Zone 1 or Zone 2 locations. Flame-proof enclosures are also known as explosion-proof enclosures. In Zone 1 and Zone 2 locations, because some exposure to flammable fluids is expected, it is assumed that flammable fluids will eventually accumulate within the flame-proof enclosure. These flame-proof enclosures are made to withstand an internal explosion so that when flammable fluids do accumulate within the enclosure, and are ignited by internal components, the flame-proof enclosure safely contains the explosion. Flame-proof enclosures are designed to contain explosions rather than to prevent them; accordingly, flame-proof enclosures do not depend on keeping flammable fluids outside the enclosure, so these enclosures typically do not employ gasket seals.
However, a problem with flame-proof enclosures is that because they are made to withstand an internal explosion, they are heavy, physically large, and relatively expensive. For example, a model EJB 106 flame-proof enclosure made from cast aluminum by Crouse Hinds, A Division of Cooper Industries, Syracuse, N.Y., weighs about 28 pounds and costs about US $600 compared to a similar sized non-flame-proof enclosure made from plastic or sheet metal that weighs about 5 pounds and costs approximately US $60. Another problem is that, while flame-proof enclosures may contain the explosion, they do not prevent an explosion. Accordingly, the components to be installed in such enclosures are generally made more robust to survive such explosions, adding to the weight, size, and cost of such components.
Accordingly, there is a need for an electrical component enclosure for use in Zone 1 or Zone 2 type locations that is lighter, smaller, and less expensive than a flame-proof enclosure. There is also a need for an electrical component enclosure that may be used in Zone 1 or Zone 2 type locations that prevents flammable fluids from igniting within the enclosure, so that smaller, lighter, and less expensive components may be installed in enclosures located in environments where a flammable fluid is expected to be present.
In Zone 2 type locations, Canadian and international electrical codes require flame-proof enclosures for electrical components which during normal operation generate sparks or have hot surfaces capable of igniting the flammable atmosphere. However, for electrical components that can only ignite the flammable atmosphere during a component failure, gasketed restricted breathing enclosures instead of flame-proof enclosures are permitted. Restricted breathing enclosures are lighter, smaller, and less expensive, compared to flame-proof enclosures. Restricted breathing enclosures may not be permitted where there may be exposure to flammable fluids such as hydrogen or acetylene which have a high diffusion rates. A problem with conventional restricted breathing enclosures is that if a concentration of a flammable fluid does accumulate inside the enclosure, there is no mechanism for reducing the concentration of the accumulated flammable fluid.
Thus electrical codes typically require flame-proof enclosures in Zone 1 type locations, and in zone 2 type locations if the electrical components may generate heat or sparks, or if the flammable fluid which may be present is one with a high diffusion rate. Accordingly, there is a need for an enclosure suitable for use in a zone 1 or 2 type location that is smaller, lighter and less expensive than a flame-proof enclosure.
An electrical component enclosure for installation in a location where a flammable fluid is expected to be present comprises:
(a) a protective housing for the electrical component, the housing having an opening formed therein which allows fluids to pass between the interior of the housing and a surrounding external atmosphere; and
(b) a catalyst associated with the opening, such that fluids passing through the opening contact the catalyst, whereby the catalyst induces the flammable fluid to react to produce a non-flammable product.
In preferred embodiments, the electrical component is selected from the group consisting of electrical switches, motor starters, motors, electrical panel boards, and electrochemical fuel cells. The enclosure is suitable for installation in a location where a flammable fluid is expected to be present at least intermittently, such as, in particular, a zone 1 or zone 2 type location.
The enclosure preferably further comprises a fluid permeable structure for supporting the catalyst. For example, the fluid permeable structure may comprise a metal mesh that allows gases and water vapor to pass therethrough. Such a metal mesh may be arranged to form a tubular column with an open end associated with the opening. The tubular column may be advantageously vertically oriented so that fluids with different densities will all contact the catalyst at some point along its vertically oriented length.
To prevent particulate contaminants from entering the enclosure, a particulate filter may be associated with the opening. The particulate filter may be a screen or another fluid permeable device that will allow liquids, such as condensed water vapor to drain from the enclosure.
To facilitate gravity draining of liquids from the enclosure, the enclosure is preferably orientable so that a drain opening is located at a low point. The drain opening preferably also serves as a breathing port. The drain/breathing port may be a hole formed in a piece of the housing or an opening formed between two adjoining pieces of the enclosure housing.
The enclosure housing preferably comprises at least two pieces which cooperate to form the housing. Preferably, the housing pieces may be separated so that electrical components contained within the housing may be accessed and/or serviced. To reduce the weight and cost of the enclosure, the protective housing pieces may be made from a thermoplastic material. Alternatively, the protective housing pieces may be made from steel or aluminum or any other suitable housing materials.
An advantage of the present enclosure is that, unlike flame-proof enclosures, the present enclosure need not be constructed to withstand an internal explosion because the catalyst prevents a combustible concentration of flammable fluid from accumulating within the enclosure housing. Thus, the present enclosure may utilize thinner and lighter housing pieces, compared to an equivalent flame-proof enclosure housing made from the same materials.
The aforementioned enclosures permit xe2x80x9cbreathingxe2x80x9d. That is, fluids are permitted to pass between the interior of the enclosure and the surrounding atmosphere. Thus sealing mechanisms are not needed between the housing pieces. However, for enclosures that employ a breathing port, it may be desirable to employ a sealing mechanism between the housing pieces so that most of the xe2x80x9cbreathingxe2x80x9d occurs through the breathing port. A sealing mechanism, such as, for example, gaskets may be used to provide sealing between adjoining housing pieces.
The present enclosures are particularly preferred for use in the presence of a flammable fluid comprising hydrogen. In this case the hydrogen is induced by the catalyst to react with oxygen to produce water. The flammable fluid may be pure hydrogen, or a hydrogen-rich fuel such as a reformate stream or natural gas. The catalyst may be any material that is capable of inducing hydrogen to react with oxygen to produce water. A catalyst comprising platinum, for example, is preferred because it is particularly efficient at inducing this reaction under the anticipated conditions within the enclosure. Preferably, the catalyst operates to induce the desired reactions without needing to be heated, and remains active in an environment where water vapor or liquid water may be present near the catalyst.
The catalyst may be mixed with an epoxy binder and applied like paint directly onto the interior surfaces of the enclosure housing, or onto a supporting substrate, such as a fluid permeable mesh. The catalyst may also be disposed on a supporting material, such as, for example, ceramic beads.
In other embodiments, an openable electrical component enclosure comprises:
(a) a housing for surrounding an electrical component capable of generating electrical discharges; and
(b) a catalyst located within the enclosure for inducing the flammable fluid to react to produce a non-flammable product.
In the case where the flammable fluid is hydrogen and the catalyst induces the reaction of hydrogen with oxygen to produce water, the amount of water produced is expected to be very small compared to the amount of water normally present in air. Accordingly, removing the product water from the enclosure is not of critical importance, and in these embodiments, the enclosure does not necessarily require an opening such as a breathing port. Furthermore, the enclosure may employ sealing mechanisms such as gasket seals between adjoining housing pieces of the enclosure.
The present enclosures are particularly suited to deployment in a power generating plant that employs electrochemical fuel cells to generate electricity. The power generating plant comprises an enclosure to protect at least one electrical component installed in a Zone 1 or Zone 2 type location. The enclosure comprises:
(a) a protective housing for the electrical component; the housing having an opening formed therein, which allows fluids to pass between the interior space of the housing and a surrounding external atmosphere; and
(b) a catalyst associated with the opening, such that fluids passing through the opening contact the catalyst, whereby the catalyst induces the flammable fluid to react to produce a non-flammable product.
A method is also provided for making an electrical component enclosure for installation in a location where a flammable fluid is expected to be present. The method comprises applying a catalyst coating to an interior surface of an enclosure housing, wherein the catalyst induces the flammable fluid to react to produce a non-flammable product.
The catalyst coating preferably comprises catalyst and a binder material that can be applied like a paint by brushing or spraying the catalyst coating mixture onto the interior housing surfaces. For catalyst coating mixtures comprising a thermosetting binder, after application onto the housing surface, the catalyst coating may be baked to cure the binder. The housing material may be plastic or metallic, but it may be advantageous to employ a metallic housing material if a high temperature is required to cure the binder.
The disclosed electrical component enclosures are designed to reduce the concentration of a flammable fluid that may accumulate within the enclosure, thereby reducing the likelihood of the flammable fluid being ignited. Accordingly, the present enclosures need not be designed to withstand an internal explosion. Thus an electrical component enclosure is provided that may be made smaller, lighter, and less expensive compared to a conventional flame-proof enclosure that would be acceptable for the same use.